Euclid has discovered the oldest quasars

A quasar is not a single star. It is the extremely bright core of a distant galaxy, where matter is falling into a supermassive black hole. The black hole itself does not emit light, but the gas and dust around it are heated and give off enormous amounts of energy. This is why quasars can shine brighter than entire galaxies.

For scientists, such objects are like cosmic beacons from the past. They help us understand how, in the early Universe, massive black holes and the first large galaxies formed so rapidly.

Details

Euclid has discovered 31 new quasars in the early Universe. Among them, 12 objects have a redshift of 7 or higher — this means we are seeing them as they were during the first approximately 770 million years after the Big Bang.

The two most ancient objects have been named EUCL J172902.75+641018.1 and EUCL J125308.55+705432.3. Their redshifts are 7.77 and 7.69 respectively. According to the ESA, this sets a new record for the oldest quasars ever observed.

Put simply, the telescope did not ‘photograph existing quasars’. It detected light that set off towards us more than 13 billion years ago. The further away an object is, the earlier stage in the history of the Universe we are seeing.

Why is this difficult?

Finding such quasars is very difficult. In the early Universe, few galaxies had yet grown large enough for a supermassive black hole to form at their centres. Moreover, their light is very faint and can resemble that of closer stars.

This is precisely where Euclid has proved particularly useful. It can survey vast swathes of the sky, detect very distant, faint objects and operate in the infrared spectrum. This helps to distinguish ancient quasars from closer light sources.

What is redshift?

Redshift is a way of understanding how far away and how ‘long ago’ we are seeing an object. The universe is expanding, and as light travels through space, its waves are stretched. The more they are stretched, the greater the redshift and the more ancient the light we are observing.

In this news story, the key figure is a redshift of z greater than 7. This means that the object dates back to a very early era of the cosmos – a time when the first galaxies and black holes were only just beginning to form actively.

Why the discovery is important

The main mystery here is this: how did supermassive black holes manage to grow so quickly? If the Universe was only 670 million years old, very little time had passed by cosmic standards. Yet the quasars were already incredibly bright, which means that very massive black holes already existed at their centres.

Previously, astronomers had mainly found the brightest and rarest ancient quasars. The new Euclid sample is significant in that it is no longer just one or two exceptional objects, but a broader ‘census’ of quasars from the cosmic dawn. ESA notes that the discovery more than doubles the number of known quasars of such antiquity.

This will help scientists better understand how the first black holes accreted mass, how galaxies formed around them, and what role such bright sources played in the early history of the Universe.

Background

Euclid is a space telescope operated by the European Space Agency. Its main objective is to study the dark Universe: dark matter, dark energy and the large-scale structure of the cosmos. To do this, it is constructing a vast three-dimensional map of the Universe, observing billions of galaxies at distances of up to 10 billion light-years and covering more than a third of the sky.

But such surveys also yield additional discoveries. Whilst Euclid is gathering data for its map of the Universe, it is also finding rare objects — including distant quasars that are too faint or too rare to be detected by smaller-scale surveys.

Source

Study: D. Yang et al., “Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8”, Astronomy & Astrophysics, 2026.